1. Field of the Invention
The present invention relates to an add-on peripheral circuit adapted to utilize the normally dedicated parallel output port interface of a general-purpose microcomputer to convey information between the peripheral circuit and the computer without requiring use of an expansion slot of the computer and without interfering with the uses to which the computer interface is normally dedicated.
2. Prior Art
General-purpose microcomputers are commonly provided with substantially dedicated interfaces and corresponding ports for connection of the more common peripherals, such as printers. To customize the system, a standard bus and expansion slots are provided for other special-purpose peripherals. The number of expansion slots may be limited, and in customizing or expanding a system most or all of them may be required for peripherals deemed absolutely necessary by the user, such as additional memory, disk controllers, internal modems, graphics enhancement, networking and so on. Consequently, the desirability of a peripheral must be weighed against the number of expansion slots already used or reserved for future use.
Many general-purpose microcomputers have internal clock/calendar circuits, chips or programs updated only when the computer is turned on. Typically, the operating system calls for the user to enter the time and date each time the operating system program is booted. Continuously updated clock/calendar circuits may be available for automatically setting the time and date but require use of an expansion slot. Although much more convenient than manually entering the time and date each time the operating system program is booted, convenience alone may not justify monopolizing an expansion slot for a continuously updated clock/calendar circuit.